Restrict parallelism in LLVM FullAOT compile, to prevent OOM (dotnet#63800)

* Restrict parallelism in FullAOT compile, to prevent OOM

* Reduce parallelism further, due to more OOM

Author: directhex

Diff for: eng/pipelines/common/templates/runtimes/run-test-job.yml

@@ -319,7 +319,7 @@ jobs:
         - script: $(Build.SourcesDirectory)/src/tests/build$(scriptExt) $(logRootNameArg)MonoAot $(monoAotBuildshCommand) $(buildConfig) $(archType) $(runtimeVariantArg)
           displayName: "LLVM AOT compile CoreCLR tests"
       - ${{ if eq(parameters.archType, 'arm64') }}:
-        - script: $(Build.SourcesDirectory)/src/tests/build$(scriptExt) $(logRootNameArg)MonoAot $(monoAotBuildshCommand) $(buildConfig) $(archType) cross $(runtimeVariantArg)
+        - script: $(Build.SourcesDirectory)/src/tests/build$(scriptExt) $(logRootNameArg)MonoAot $(monoAotBuildshCommand) $(buildConfig) $(archType) cross $(runtimeVariantArg) -maxcpucount:2
           displayName: "LLVM AOT cross-compile CoreCLR tests"
           env:
             __MonoToolPrefix: aarch64-linux-gnu-

Diff for: eng/pipelines/runtime.yml

@@ -1110,8 +1110,7 @@ jobs:
     runtimeFlavor: mono
     platforms:
     - Linux_x64
-    # Disabled pending outcome of https://github.com/dotnet/runtime/issues/60234 investigation
-    #- Linux_arm64
+    - Linux_arm64
     helixQueueGroup: pr
     helixQueuesTemplate: /eng/pipelines/coreclr/templates/helix-queues-setup.yml
     jobParameters: